[PATCH] Documentation, intel_pstate: Add a better description of the intel_pstate legacy mode internal governors

* [PATCH] Documentation, intel_pstate: Add a better description of the intel_pstate legacy mode internal governors
@ 2015-06-01 13:36 Prarit Bhargava
  2015-06-02  4:02 ` Viresh Kumar
  2015-06-04 22:51 ` Jonathan Corbet
  0 siblings, 2 replies; 5+ messages in thread
From: Prarit Bhargava @ 2015-06-01 13:36 UTC (permalink / raw)
  To: linux-kernel
  Cc: Prarit Bhargava, Jonathan Corbet, Rafael J. Wysocki,
	Kristen Carlson Accardi, Dirk Brandewie, linux-doc, Viresh Kumar,
	x86

This patchset was originally submitted and acked here

http://marc.info/?l=linux-kernel&m=140203008832333&w=2

but lost at some point.

P.

----8<----

The current documentation is incomplete wrt the intel_pstate legacy
internal governors.  The confusion comes from the general cpufreq
governors which also use the names performance and powersave.  This patch
better differentiates between the two sets of governors and gives an
explanation of how the internal P-state governors behave differently from
one another.

Also fix two minor typos.

Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Cc: Kristen Carlson Accardi <kristen@linux.intel.com>
Cc: Dirk Brandewie <dirk.j.brandewie@intel.com>
Cc: linux-doc@vger.kernel.org
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: x86@kernel.org
Signed-off-by: Prarit Bhargava <prarit@redhat.com>
---
 Documentation/cpu-freq/governors.txt    |    2 +-
 Documentation/cpu-freq/intel-pstate.txt |   21 +++++++++++----------
 2 files changed, 12 insertions(+), 11 deletions(-)

diff --git a/Documentation/cpu-freq/governors.txt b/Documentation/cpu-freq/governors.txt
index 77ec215..c15aa75 100644
--- a/Documentation/cpu-freq/governors.txt
+++ b/Documentation/cpu-freq/governors.txt
@@ -36,7 +36,7 @@ Contents:
 1. What Is A CPUFreq Governor?
 ==============================
 
-Most cpufreq drivers (in fact, all except one, longrun) or even most
+Most cpufreq drivers (except the intel_pstate and longrun) or even most
 cpu frequency scaling algorithms only offer the CPU to be set to one
 frequency. In order to offer dynamic frequency scaling, the cpufreq
 core must be able to tell these drivers of a "target frequency". So
diff --git a/Documentation/cpu-freq/intel-pstate.txt b/Documentation/cpu-freq/intel-pstate.txt
index 6557507..be8d400 100644
--- a/Documentation/cpu-freq/intel-pstate.txt
+++ b/Documentation/cpu-freq/intel-pstate.txt
@@ -3,24 +3,25 @@ Intel P-state driver
 
 This driver provides an interface to control the P state selection for
 SandyBridge+ Intel processors.  The driver can operate two different
-modes based on the processor model legacy and Hardware P state (HWP)
+modes based on the processor model, legacy mode and Hardware P state (HWP)
 mode.
 
-In legacy mode the driver implements a scaling driver with an internal
-governor for Intel Core processors.  The driver follows the same model
-as the Transmeta scaling driver (longrun.c) and implements the
-setpolicy() instead of target().  Scaling drivers that implement
-setpolicy() are assumed to implement internal governors by the cpufreq
-core. All the logic for selecting the current P state is contained
-within the driver; no external governor is used by the cpufreq core.
+In legacy mode, the Intel P-state implements two internal governors,
+performance and powersave, that differ from the general cpufreq governors of
+the same name (the general cpufreq governors implement target(), whereas the
+internal Intel P-state governors implement setpolicy()).  The internal
+performance governor sets the max_perf_pct and min_perf_pct to 100; that is,
+the governor selects the highest available P state to maximize the performance
+of the core.  The internal powersave governor selects the appropriate P state
+based on the current load on the CPU.
 
 In HWP mode P state selection is implemented in the processor
 itself. The driver provides the interfaces between the cpufreq core and
 the processor to control P state selection based on user preferences
 and reporting frequency to the cpufreq core.  In this mode the
-internal governor code is disabled.
+internal Intel P-state governor code is disabled.
 
-In addtion to the interfaces provided by the cpufreq core for
+In addition to the interfaces provided by the cpufreq core for
 controlling frequency the driver provides sysfs files for
 controlling P state selection. These files have been added to
 /sys/devices/system/cpu/intel_pstate/
-- 
1.7.9.3


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